1. Field of the Invention
This invention relates to a super-compact motor designed for a high output and high efficiency.
2. Related Background Art
As what is formed as a compact motor, there is, for example, a compact cylindrically-shaped step motor as shown in FIG. 12 of the accompanying drawings. A stator coil 105 is concentrically wound on a bobbin 101, which is axially sandwiched and fixed between two stator yokes 106, on which stator teeth 106a and stator teeth 106b are alternately disposed in the circumferential direction of the inner diametral surface of the bobbin 101, and the stator yokes 106, integral with the stator teeth 106a or 106b, are fixed to cases 103, whereby a stator 102 is constructed.
A flange 115 and a bearing 108 are fixed to one of the two sets of cases 3, and another bearing 108 is fixed to the other case 103. A rotor 109 comprises a rotor magnet 111 fixed to a rotor shaft 110, and the rotor magnet 111 cooperates with the stator yokes 106 of the stator 102 to form radial clearance portions. The rotor shaft 110 is rotatably supported between the two bearings 108.
The above-described compact step motor according to the prior art, however, suffers from the disadvantage that the output thereof does not become high because a magnetic flux created by the supply of electric power to the stator coil 105 does not effectively act on the rotor magnet 111 for it to pass chiefly the end surface 106a1 of the stator teeth 106a and the end surface 106b1 of the stator teeth 106b, as shown in FIG. 13 of the accompanying drawings.
The applicant of the basic application filed in Japan proposed in U.S. Pat. No. 5,831,356 a motor which solved such a problem.
This proposed motor is constructed such that a rotor comprising a permanent magnet, circumferentially equally divided and alternately magnetized to different poles, is formed into a cylindrical shape, and a first coil, a rotor and a second coil are disposed axially of the rotor in the named order, and a first outer magnetic pole and a first inner magnetic pole excited by the first coil are opposed to the outer peripheral surface and inner peripheral surface, respectively, of the rotor, and a second outer magnetic pole and a second inner magnetic pole excited by the second coil are opposed to the outer peripheral surface and inner peripheral surface, respectively, of the rotor, and a rotary shaft, which is a rotor shaft is taken out of the cylindrically-shaped permanent magnet.
The motor of such a construction is high in output and the outer dimension thereof can be made small, but the diametral dimensions of the inner magnetic poles are small and therefore, the working of the magnetic pole teeth thereof is difficult, and it has been desired that a fluctuation-free stable output be obtained from a motor of a small diametral dimension.
Therefore, the applicant of the basic application filed in Japan has recently proposed in U.S. patent application Ser. No. 08/994,994 a motor in which the shape of inner magnetic poles is a shape of good workability, and a rotor, in which output transmitting means such as gears and pulleys can be easily mounted on a rotary shaft of a small diametral dimension and from which a fluctuation-free stable output can be obtained, has been proposed in U.S. patent application Ser. No. 09/022,474.
Further, it has recently been desired to provide a motor which is constructed super-compactly and yet has a higher output and high efficiency.